In order to elucidate the metabolism of the systemic insecticide, phosphamidon (2-chloro-2-diethylcarbamoyl-1-methylvinyl dimethyl phosphate), treated to pine trees against pine leaf gall midges (Thecodiplosis japonensis Uchida et Inouye), [vinyl, carbonyl-^(14)C] phosphamidon was implanted into the trunks of 10-year-old Korean red pine (Pines densiflora Sieb. et Zucc.) and Japanese black pine (Pinus thunbergii Parl.), respectively. This chemical was degraded very quickly in pine trees after implanting, as confirmed by TLC/autoradiography of the extracts of pine needles. Phosphamidon metabolites in phosphate buffer extracts of pine needles include the major metabolite, α-chloroacetoacetic acid diethyl-amide, α-chloroacetoacetic acid ethylamide, 3-hydroxy-N,N-diethylbutanamide, acetoacetamide, and trimethyl phosphate. The metabolism within pine trees is expected to be similar to this. Based on these findings, it is believed that the major pathway leading to the metabolites would be related to the P-O-vinyl hydrolysis of the chemical structure.